Practice: Shooter

Set the goal up front. This mirrors the frcdesign shooter practice but in Fusion. Tell them they are NOT designing from scratch — the geometry and ratios are given. The point is to practice the Fusion workflow: components, bodies, joints, and inserting vendor parts. A flywheel shooter grabs a game piece, pins it against a hood, and flings it. Flywheel speed and compression set the shot.

Demo creating User Parameters live — this is the Fusion equivalent of Onshape Variables. Stress saving immediately so Fusion's cloud versioning kicks in. Common mistake: typing a unit in the expression wrong (use 4in not 4 in). Parameters let them change one number and have the whole model update — show that you can type flywheelDia anywhere a dimension is expected.

Hammer the habit: Assemble > New Component BEFORE sketching. Everything in its own component is what makes joints work later. The #1 beginner mistake in Fusion is modeling all bodies in the root — then nothing can be jointed. Tube bolt holes are typically 1in spacing on a 2x1. Rename components as you go so the browser stays readable.

1.125in is the standard FRC bearing OD pocket. Show Insert > Insert Derive / Insert McMaster or dragging a downloaded STEP into the design. This replaces Onshape's MKCad library — in Fusion you download the STEP from REV/AndyMark and insert it. Concentricity matters: if the two bearing bores don't line up, the shaft binds. Use a construction axis through both.

Use the hex profile from a sketch — Fusion has no built-in hex shaft, so they sketch a 0.5in across-flats hexagon. The flywheel bore must be hex too so it drives off the shaft, not a press fit. Reference the flywheelDia parameter for the OD. Common mistake: extruding the flywheel as round-bore — then it can't transmit torque. Hex bore = positive drive.

Demo the built-in SpurGear add-in (Utilities > Scripts and Add-Ins, or Tools) — this is the Fusion stand-in for Onshape's FeatureScript gear. 21/14 = 1.5, our ratio. Center distance for 20DP: (14+21)/2/20 = 0.875in between shaft centers. Have them verify the motor mounting holes don't collide with the flywheel. This is where ratios become real — small gear on motor = reduction.

Insert the actual NEO (REV) or Kraken (WCP/CTRE) STEP — real motor body matters for collision checks. The hood gap (compression) is the single biggest performance variable: ~1in means the game piece gets squeezed and grips the flywheel. Too tight = jam, too loose = no spin transfer. Have them offset the hood arc from the flywheel OD so the gap is parametric.

This is the core Fusion skill. Ground the backplate first. Rigid joint = parts that don't move relative to each other (Onshape 'Fastened mate'). Revolute joint = the one spinning axis (Onshape 'Revolute mate'). Only the flywheel shaft + gear + flywheel get a revolute joint. Common mistake: jointing to the root body instead of components — joints need two component faces/edges. Drag the revolute joint to confirm it spins freely without collision.